Generally, an ultrasonic diagnostic apparatus is for performing a diagnosis such that ultrasonic waves are transmitted into a body of an object from an ultrasonic probe (hereinafter, simply referred to as a probe), a reflected echo signal of the ultrasonic waves which have been reflected from the inside of the body is received by the probe, and an image or the like which is suitable for the test of a tissue, a function, or the like inside the body is created based on the received reflected echo signal (RF signal).
In such an ultrasonic diagnostic apparatus, for the test by a B mode image, it is preferable to obtain an image with a high image quality by placing the probe on the object with a relatively strong force, pressing and deforming the body tissue so that the deep tissue can be closer to the probe, and imaging the tissue since the ultrasonic waves attenuate in the course of the propagation inside the body tissue. On the other hand, in the bloodstream test such as the Doppler measurement, the CFM, or the like, since it is not possible to obtain correct information on the bloodstream because the cross-section of the blood vessel is deformed when the probe is placed on and pressed against the body tissue with an excessively strong force, it is preferable to perform the test with the pressurizing state which is gentler than that at the time of the B mode diagnosis. In addition, since the body tissue has a nonlinearity in which the hardness of the tissue changes in accordance with the strength of the pressurizing even in the test by elastography for creating an image of elastic information regarding the hardness or the softness of the body tissue, it is important to perform a diagnosis based on an elasticity image obtained under a pressurizing state with a constant absolute pressure.
Accordingly, it is preferable to measure and display the absolute pressure applied to the body tissue in real time since there is a concern that an appropriate prompt diagnosis is hindered if the test proceeds in an inappropriate pressurizing state in various testing methods or when the testing method is changed, for example.
In order to measure an actual pressure to be applied to the body tissue of the object, that is, an absolute pressure to be applied to the body tissue (hereinafter, simply referred to as an absolute pressure), Patent Literature 1 discloses that the distortion of an elastic coupler is obtained with the use of a known displacement and distortion calculation based on a pair of RF signal frame data, which was obtained at different timings, and the obtained distortion is converted into the absolute pressure with the use of a pre-set elastic modulus of the elastic coupler.
Thus, according to the method of calculating the pressure disclosed in Patent Literature 1, it is possible to obtain the elastic information on the hardness or the softness of the body tissue by measuring the absolute pressure applied to the object, for example.